0-30 Vdc Stabilized Power Supply

[Staigen]

Hi there Sasa G

Check R11 and R12

//Staigen

[kankundachi]

Hi audioguru :

  I have found the reason of the minimize current is 670mA. Because R20 original value is 10K,but my circuit is 2.2K. :P After change the R20,the minimize current is 9.1mA,but maximum current is 4.0A.  ??? How about your opinion? And,I will upload my schematic,as below attached file. Please you double check my schematic. Thank you very much.  :)


Best Regards,

              Stanley

Power_supply.pdf

[audioguru]

Hi Stanley,
I'm glad you fixed your problem.
I had a quick look at your schematic, but it is difficult to compare with other schematics because you changed all the parts numbers.

I think your output will be full of ripple at high current and with voltage settings more than about 25V, because the transformer voltage isn't 30V.
Your single 2N3055 output transistor will be extremely hot and might fail at high current and low voltage output.

Why use an output fuse? Its resistance in series with the load ruins the fabulous voltage regulation of the circuit. If you worry that the single 2N3055 might short when it gets too hot then add a second one in parallel and emitter resistors for both. They will share the heating.

Why use a current meter in series with the output? Its resistance also ruins the fabulous voltage regulation of the circuit. If you can remove the shunt on the one you have, you can make a low-voltage voltmeter out of it by adding a resistor in series with its coil and having it measure the voltage across the original circuit's R7. 1A through the 0.47 ohms equals 0.47V across it.

You can reduce your max current of 4A down to about 3A by changing the original circuit's R18 to 68k.
You can reduce the minimum output current by shorting the original circuit's R17.

You are clever to use 44V supply-rated LM741A opamps for the ones with a 42V supply in your project. The "A" also has a nice low input offset voltage. ;D

[kankundachi]

Hi audioguru :

    Thank you for your kindly reply. I will follow your opinion and try it. ;D


Best Regards,

                Stanley

[cyw1984]

hello all
I want to know the voltag range of

[audioguru]

Hi Cyw,
The output of U1 is an 11.2V voltage reference, and the pots just divide it down. The voltage range is easy to calculate.
However, the lower end of R17 has the voltage developed across R7 (caused by output current) adding a negative voltage to R17.

To use another control voltage instead of the existing one that is used to control the current, you would need to re-arrange the inputs of U3 and add an inverting opamp stage.

[cyw1984]

Hi Cyw,
The output of U1 is an 11.2V voltage reference, and the pots just divide it down. The voltage range is easy to calculate.
However, the lower end of R17 has the voltage developed across R7 (caused by output current) adding a negative voltage to R17.

To use another control voltage instead of the existing one that is used to control the current, you would need to re-arrange the inputs of U3 and add an inverting opamp stage.

o..I SEE
Firstly, i should remove all the part of U1 (11.2V),Right??

I wolud like to use another control voltage reference (DAC) instead of the existing one that is used to control the current and voltage.

Also...How to re-arrange the inputs of U3 and add an inverting opamp stage.
Can you draw it to me??? Thanks a lot

[audioguru]

Firstly, i should remove all the part of U1 (11.2V),Right??

Yes.

I wolud like to use another control voltage reference (DAC) instead of the existing one that is used to control the current and voltage.

Also...How to re-arrange the inputs of U3 and add an inverting opamp stage.
Can you draw it to me???

I think this will work:

[cyw1984]

Yes.


I think this will work:

Thanks~~But I need add on a NEW shockky or not??
What NEW Op amp should I add on this circuit??

and pin 3 of U3 and NEW op amp connect to where??? thanks

[audioguru]

Thanks~~But I need add on a NEW shockky or not??

What is a "schokky"?
This project doesn't use nor need a high-speed, high-leakage Shottky diode for D9. It is an ordinary 1N4148 diode.

What NEW Op amp should I add on this circuit??

Use the same kind of opamp with a high supply voltage rating as U3.

and pin 3 of U3 and NEW op amp connect to where???

Can't you see the PNG schematic I posted? Download and save the pic and open it in a viewer program. It will be very clear. Here it is as a GIF:

[HelderS]

Hi, everyone, I've completed the Power Supply 0-30V @ 0,002 - 3A, but i've done a stupid mistake, i have turned it on before putting the ICs in the respective sockets, sou when I turned it on, the PS made a sound, wich I think, came from a capacitor. I've cut the power off right after, but after inserting the ICs, happened this strange thing, the PS turns on the Led (Current Limit) and never turns off. Maybe I 've burned the transistor Q3??

[audioguru]

Hi Helder,
Welcome to our forum. ;D
There is nothing in the circuit that would break if the circuit was powered without the ICs installed. You can check Q3 by shorting its base to its emitter. If the LED turns off then the transistor is OK.
Did you use high-supply-voltage rated opamps as discussed here?
Did you use a 30V transformer?
Did you substitute any parts?

[cyw1984]

What is a "schokky"?
This project doesn't use nor need a high-speed, high-leakage Shottky diode for D9. It is an ordinary 1N4148 diode.


Use the same kind of opamp with a high supply voltage rating as U3.


Can't you see the PNG schematic I posted? Download and save the pic and open it in a viewer program. It will be very clear. Here it is as a GIF:

output 0V mean that common pin 3 and  short  to GOUND???

[audioguru]

The project doesn't have a ground. It has a common voltage in its rectifier circuit and a 0V terminal on its output. Pin 3 of U3 is shown on my "0-30V external control" schematic. Pin 3 of the new opamp connects to the output 0V terminal with the other few parts that are connected there. The new opamp measures the voltage across R7, which is caused by output current. ;D

[Gruber]

Hi.
i decided to try making this power supply.I almost got all of the parts as described in the scheme.
But have several questions ( i read most of the posts in this topic,but the 44 pages can drive reader sometimes to confusion :P ).
I got the standart TL081 and i hope this wont be a problem.The 2N2219 are replaced by TIP41A,as mentioned before.I'll try to find resistors with higher power (5W+) and the C1 is 10000,0/63V.
The transformer is ~26V 3,5A and i hope it'll handle the (eventual) 3A/30V load.
But the questions are :
1.Can i use for Q4 "high powered" transistor? Something like 15A 200V+ and around 150W ? I got one of that  from a friend building 1kW+ power amplifier and i hope one of those transistors can handle the load itself.The transistor itself is 2sc5200 from "fairchald" or something like this (sorry,cant remember correct).I saw the post about linking two 2N2055 in parallel,but decided to use single "high powered" transistor.
2.I read in past reply that using a (digital) ampermeter connected to this power supply is not recommended because will cause malfunction of the scheme.Where should i connect the ampermeter ? And what about the voltmeter - will it cause problems too if connected to the output of the scheme ? I am planning to use the digital voltmeter/ampermeter listed in project's section of the site

3. and the most important question for me - does anyone have an idea how to controll the output voltage digitaly ? Not with the standart linear potentiometers,but digital ?
I saw that Analog devices and Microchip have digital potentiometers,but either i cant find them in local stores (like the good looking AD5228),or they require some kind of "SPI" controllers,which are quite infamilliar to me.
I am trying to build one good power supply with some extras - like the digital controlled output voltage.Unfortunately i cant find any good schematic about digital controlling of some values,neither i can find the AD5228 digital potentiometer.
Any help will be welcome.

[audioguru]

I got the standard TL081 and i hope this wont be a problem.

Your 26V transformer might be 28V without a load. It will produce a rectified and filtered positive supply of about 38V, plus the negative supply of 5.6V equals nearly 44V across the TL081 opamps that are rated for an absolute max supply voltage of only 36V. It is risky.

The 2N2219 are replaced by TIP41A

More than enough since a TIP31A is fine.

the C1 is 10000,0/63V.

Excellent.

The transformer is ~26V 3,5A and i hope it'll handle the (eventual) 3A/30V load.

As was said in these 44 pages, only 26VAC isn't enough for this project to produce 30V at full current. You might get 27V then any higher settings will result in plenty of ripple.

But the questions are :
1.Can i use for Q4 "2sc5200"?

It is a good transistor but must dissipate over 100W at 3A and a low output voltage setting or short. It will be at its max temperature limit if it was cooled "perfectly" with a 150W dissipation but maybe will be OK with an enormous finned heatsink with thermal grease, no insulator and a high velocity fan.

2.I read in past reply that using a (digital) ampermeter connected to this power supply is not recommended because will cause malfunction of the scheme.Where should i connect the ampermeter ? And what about the voltmeter - will it cause problems too if connected to the output of the scheme ? I am planning to use the digital voltmeter/ampermeter listed in project's section of the site

The meters must use a power supply separate from what they are measuring. The shunt resistance of the current-meter will ruin the excellent voltage regulation of the project. Instead, I would arrange a voltmeter to measure the voltage across the project's current sensor, R7, then scale the voltage into Amps.

3. and the most important question for me - does anyone have an idea how to controll the output voltage digitaly ? Not with the standart linear potentiometers,but digital ?
I saw that Analog devices and Microchip have digital potentiometers,but either i cant find them in local stores (like the good looking AD5228),or they require some kind of "SPI" controllers,which are quite infamilliar to me.
I am trying to build one good power supply with some extras - like the digital controlled output voltage.Unfortunately i cant find any good schematic about digital controlling of some values,neither i can find the AD5228 digital potentiometer.
Any help will be welcome.

See the recent discussion with cyw1984 who will control his project with a DAC, and my modification to the circuit which allows it. If you want to use a digital pot instead, many manufacturers make them with a button to step up and another button to step down. ;D

[Gruber]

thanks for the fast reply audioguru.
i'll try to find some new replacements for the TL081.I think i checked some of those posted here,but couldnt find them in local stores.Which means i have to search for another replacements.

The transformer is "custom made" and should have max 3,5A at 26V with some aditional Amperage as a reserve.It has more VA than should be used and i hope it an take some "pressure".
But i dont think i'll need 3A load at 30V,so even 20-24 should be fine :)

About the 2sc5200 - it seems i have to connect two of them after all.I am planning to use some good heat sinks,but i cant afford to dissipate too much heat.

I didnt get the part with the ampermeter...so i should connect a voltmeter in paralel with R7 and measure the voltage and them scale it into Amps ? It will be interesting to do it with digital one :)

And about the digital regulating - i will check the previous posts about it,but i think i will have some questions about it too :)

[audioguru]

I didnt get the part with the ampermeter...so i should connect a voltmeter in paralel with R7 and measure the voltage and them scale it into Amps ?

Correct. The resistance of an ammeter in series with the load would cause a voltage drop at the load. You don't want a voltage drop with a regulated supply. R7 is not in series with the load but is in series with the supply to the project so doesn't affect voltage regulation. Ohm's Law says that the voltage across R7 is a multiple of the current in the load. ;D

[kankundachi]

Hi audioguru :

  I have fixed my 0-30 Vdc Stabilized Power Supply. It works very nice. Thank you for your kindly support at this period. Besides I have changed the R18 & R11 to VR100K & VR50K. Because the VR100K can be fine tune the current to 3A , VR50K can be fine tune the voltage to 30V. And I have modified my schematic is as below attached file. Thank you again.  ;D


Best Regards,

            Stanley

Power_supply.pdf

[audioguru]

Hi Stanley,
Excellent! ;D
You have a good idea to use trimpots for fine tuning.

[audioguru]

Hi Helder,
Yeah, the problems with this project are frustrating. I would have updated it but I don't need it. A few people have built the improved one with success so maybe I'll update the project.

It is a kit. Maybe errors were made on purpose in its schematic and parts list so that copies won't work. Maybe it would be replaced by a better or improved one if you built the kit and complained about it.

[kankundachi]

Hi HelderS :

    About your opinion,I can realize your feeling.But I think everyone to bring up his experience in this project is very good.Because it will be make this project to tend to perfect.Besides we can study this project by everyone experience.Isn't it? :)


Best Regards,

              Stanley

[HelderS]

Ok, my BC557 have already arrive. So, i've put him at his place, and turned on my PS, but I'm having a doubt wich is, how can I measure the output current ??

I've built my PS entirely original, I've done none of the changes proposed in this forum... (I thought the project on the website was CORRECT)

[audioguru]

Hi Helder,
A current meter is made by using a low-value resistor in series with the load, and measuring the voltage created across it. R7 in the circuit is already in series with the circuit, so the voltage drop across it is caused by load current through it, but its voltage drop doesn't reduce the output voltage like a current meter in series with the load would.

Connect you voltmeter across R7 to measure load current. Ohm's Law says that 2A through the 0.47 ohms of R7 creates a voltage drop across it of 0.94V, 1A creates 0.47V, 100mA creates 0.047V etc.

Many projects on the web have obsolete parts, parts backwards or schematics with shorts on them. Unfortunately, this project is one of them but we recently designed fixes for it. ;D

[HelderS]

Hi, Audioguru, sorry about the stupid question, but to measure the voltage in R7, I have to short circuit the output, right? That's What I've done, and I measure at R7, a voltage of 0.022 V. wich gives 46.8 mA. What's wrong? Why can't I have more than that measured current (46.8 mA) ?